Three-dimensional printing process for producing a self-destructible temporary structure

ABSTRACT

The invention relates to additive manufacturing (AM) and in particular to a degradable material for use in applications that require temporary structure stability, such as in investment casting or biomedical applications or as a temporary support material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent ApplicationNo. 61/182,778, filed Jun. 1, 2009.

FIELD OF THE INVENTION

The invention relates to additive manufacturing (AM) and in particularto a degradable material for use in applications that require temporarystructure stability, such as in investment casting or biomedicalapplications or as a temporary support material.

BACKGROUND OF THE INVENTION

AM is generally a process in which three-dimensional (3D) objects areconstructed utilizing a computer model of the objects. These processesare used in various fields, such as design related fields for purposesof visualization, demonstration and mechanical prototyping.

Various techniques of AM exist, one such technique, otherwise known as3D printing, being performed by a layer by layer inkjet deposition ofbuilding materials. Depending on the building materials, the layers arethen cured or solidified. The building materials may include modelingmaterials and support materials, which form the object and the temporarysupport constructions supporting the object as it is being built. Incases where objects include overhanging features or shapes, e.g. curvedgeometries, negative angles, voids, and so on, objects are typicallyconstructed using adjacent support constructions, which are used duringthe printing and then subsequently removed in order to reveal the finalshape of the fabricated object.

During the AM process, at least one material (“object material” or“modeling material”) is deposited to produce the desired object and atleast one other material (“support material”) to provide support forspecific areas of the object during building and assure adequatevertical placement of subsequent object layers. Both materials, modelingmaterial and support material might be initially liquid and aresubsequently hardened to form the required layer shape. The hardeningprocess may be performed by a variety of methods, such as UV curing,phase change, crystallization, drying, etc. In all cases, the supportmaterial is deposited in proximity of the object layers and often formscomplex geometries and fills object voids.

In such cases, the removal of the support structure is difficult andtime consuming, and may damage the formed object.

Examples of materials used as support materials are soluble materialsand phase change materials.

Soluble support materials are especially appropriate for supportingsmall parts, because large masses of soluble material may require longperiod of time for dissolving.

To diminish such problems, the fabricated object is often immersed inwater or in a solvent that is capable of dissolving the supportmaterials. In many cases, however, the cleaning process may involvetoxic materials, manual labor and special equipment requiring trainedpersonnel, protective clothing and expensive waste disposal. Inaddition, the dissolving process is usually limited by diffusionkinetics and may require very long periods of time, especially when thesupport constructions are large and bulky.

Other examples of support material presently used in some AM techniquesare phase change materials. These, at an appropriately high temperature,melt and thus permit support removal in the liquid state. One of thedrawbacks of the phase change is that the temperature required formelting the support material tends to cause deformation of the modelstructure.

Another example of an application that requires materials that can beeasily removed is investment casting. In investment casting thesematerials are used for mold preparation and then removed, usually bymelting, evaporation or burning in order to allow casting of anothermaterial, for example a metal.

In addition, in biomedical applications it would be beneficial to beable to produce temporary objects which are destructible or degradable,for use, for example, as temporary implants or drug delivery devices.

It would therefore be advantageous to have a material and process for AMmanufacturing enabling easy, inexpensive, fast and convenient formationof self destructible objects.

SUMMARY OF THE INVENTION

This invention is directed to a combination of a degradable materialsolution that comprises a degradable component and may comprise otheragents, and a disintegrating agent solution that comprises adisintegrating agent and may comprise other agents, for a threedimensional printing process, wherein the degradable material solutionmay be combined with the disintegrating agent solution before, during orafter material deposition in the three dimensional printing process.

This invention is further directed to an embodiment, wherein thedegradable component is degraded by the disintegrating agent after thedegradable material solution is hardened or solidified. Further, thisinvention is directed to a self degradable material produced by 3Dprinting, wherein the degradable material comprises a degradablecomponent and a disintegrating agent, where the degradable component andthe disintegrating agent are combined and wherein the degradablecomponent is a molecular structural element, which is chemicallydisassembled by the disintegrating agent.

According to the present invention, the degradable component may be acopolymer, a block-copolymer, a photopolymer, a polysaccharide, reactivepolymer-protein hybrid molecules, a biosynthetic hydrogel material or awax.

According to some embodiments, the copolymer contains polyethyleneglycol(PEG), poly(acrylic acid), poly(hyaluronic acid), polycaprolactone orpoly(vinyl alcohol).

According to further embodiments, the disintegrating agent is an enzyme,an acid, a base or a catalyst. Additionally, the enzyme may be anesterase, such as a lipase, a cellulase, or a dextranase.

According to some embodiments of this invention, the disintegratingagent is in an isolated state, for example, is inactive or isencapsulated.

According to further embodiments, the degradable material solution andthe disintegrating agent solution may further comprise any one of areactive solvent, a non-reactive solvent, a surfactant, aphotoinitiator, a viscosity modifier, a rheology modifier or anycombination thereof.

According to one embodiment, the degradable component is degraded by thedisintegrating agent within one to 72 hours.

According to some embodiments, the combination of the degradablematerial solution and the disintegrating agent solution is controlled bya dedicated software so that the volume ratio of the degradable materialsolution and the disintegrating agent solution can be modulated duringthe three dimensional printing process.

According to certain embodiments, the disintegrating agent solutioncomprises a solvent that is incompatible with a solvent included in thedegradable material solution. According to further embodiments, thedisintegrating agent solution is polymerized and releases thedisintegrating agent by diffusion.

This invention further relates to a method for preparing a combinationof a degradable material solution that comprises a degradable component,and a disintegrating agent solution that comprises a disintegratingagent, for a three dimensional printing process, said method comprising:providing the degradable material solution; providing the disintegratingagent solution; and combining said degradable material solution and saiddisintegrating agent solution; wherein after the degradable materialhardens it is degraded by the disintegrating agent.

According to certain embodiments, the degradable material solution andthe disintegrating agent solution are combined in a mixing chamberbefore jetting in the three dimensional printing process.

According to further embodiments, the degradable material solution andthe disintegrating agent solution are combined during the threedimensional printing process by combining the degradable materialsolution and the disintegrating agent solution on a printing tray orsurface upon which a three dimensional pattern is being printed.

The invention is further directed to embodiments wherein the degradablematerial solution and the disintegrating agent solution are combinedafter jetting in the three dimensional printing process.

According to certain embodiments of the invention the disintegratingagent is in an isolated state and the disintegrating agent is releasedand/or activated during or after the three dimensional printing processby an external trigger.

According to certain embodiments, the volume ratio of the degradablematerial solution and the disintegrating agent solution is determined bya dedicated software.

According to further embodiments, a dedicated software together with adedicated automated pump system and an appropriate mixing chamberdynamically produce a homogeneous mixture of the degradable materialsolution with between 0.01% (v/v) and 10% (v/v) of the disintegratingagent solution, which is delivered from a cartridge and mixed with thedegradable material solution in the mixing chamber before jetting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: schematically describes a system wherein the degradable materialsolution (3) and the disintegrating agent solution (4), found initiallyin cartridges (7) and pumped therefrom via pumps (5) and (6), are mixedon the printing tray (10) after deposition from printing heads (1) and(2), thereby preparing the printed object (9). As shown in FIG. 1,computer (8) regulates the deposition of degradable material solution(3) and the disintegrating agent solution (4) from cartridges (7);

FIG. 2: schematically describes a system wherein the degradable materialsolution (3) and the disintegrating agent solution (4), found initiallyin cartridges (7) and pumped therefrom via pumps (5) and (6), are mixedin a dedicated mixing chamber (11) immediately before entering theprinting head (1) for deposition, thereby preparing the printed object(9) on printing tray (10). As shown in FIG. 1, computer (8) regulatesthe pumping of degradable material solution (3) and the disintegratingagent solution (4) from cartridges (7) via pumps (5) and (6) into mixingchamber (11);

FIG. 3: schematically describes a system wherein the degradable materialsolution together with the encapsulated disintegrating agent (12) aremixed within the cartridge (7). They are then pumped via pump (5) fromcartridge (7) to printing head (1), wherefrom they are deposited onprinting tray (10), thereby preparing printed object (9);

FIG. 4: presents a graph of stiffness vs. time relating to the automatedscheduling of degradation;

FIG. 5: shows the degradation of PCL specimens added to Pseudomonaslipase solutions after two hours of incubation, in comparison to PCLspecimens added to candida lipase and porcine pancreas lipase solutions,which did not degrade within two hours;

FIG. 6: demonstrates the synthesis of triblock polymers PCL-PEG-PCL fromPEGs of various lengths and E-Caprolactone, in the presence of Stannous2-Ethyl-Hexanoate;

FIG. 7: shows the shear rate sweep tests of three different polymersolutions at 25° C.;

FIG. 8 a: shows the time sweep tests at a temperature of 25° C. at ashear rate of 10sec-1 of three different polymer solutions;

FIG. 8 b: shows the time sweep tests at a temperature of 25° C. at ashear rate of 50sec-1 of three different polymer solutions;

FIG. 8 c: shows the time sweep tests at a temperature of 40° C. at ashear rate of 10sec⁻¹ of three different polymer solutions;

FIG. 9: shows the time sweep tests of three different polymer solutionsat a temperature of 25° C. at a shear rate of 10sec⁻¹, after theaddition of 0.1 mg/ml lipase;

FIG. 10: shows the viscosity variation of PEG_(6000Da) triblock afterthe addition of various lipase doses, specifically, no lipase, 0.1 mg/mllipase and 1.0 mg/ml lipase;

FIG. 11 a: shows the viscosities of PCL_(1000Da)PEG_(4000Da)PCL_(1000Da)after acrylation compared to support material;

FIG. 11 b: shows the viscosities of PCL_(1000Da)PEG_(4000Da)PCL_(1000Da)before acrylation compared to support material;

FIG. 12 a: shows the shear rate sweep test of 20% solutions ofPCL_(500Da)PEG_(4000Da)PCL_(500Da) andPCL_(750Da)PEG_(1500Da)PCL_(750Da) before acrylation;

FIG. 12 b: shows the shear rate sweep test of 20% solutions ofPCL_(500Da)PEG_(4000Da)PCL_(500Da) andPCL_(750Da)PEG_(1500Da)PCL_(750Da) after acrylation;

FIG. 13 a: shows the time sweep test of 20% solutions ofPCL_(500Da)PEG_(4000Da)PCL_(500Da) andPCL_(750Da)PEG_(1500Da)PCL_(750Da), compared to the support, beforeacrylation at 25° C.;

FIG. 13 b: shows the time sweep test of 20% solutions ofPCL_(500Da)PEG_(4000Da)PCL_(500Da) andPCL_(750Da)PEG_(1500Da)PCL_(750Da), compared to the support, afteracrylation at 25° C.;

FIG. 13 c: shows the time sweep test of 20% solutions ofPCL_(500Da)PEG_(4000Da)PCL_(500Da) andPCL_(750Da)PEG_(1500Da)PCL_(750Da), compared to the support, afteracrylation at 40° C.

DESCRIPTION OF THE INVENTION

The following description is presented to enable one of ordinary skillin the art to make and use the invention as provided in the context of aparticular application and its requirements. Various modifications tothe described embodiments will be apparent to those with skill in theart, and the general principles defined herein may be applied to otherembodiments. Therefore, the present invention is not intended to belimited to the particular embodiments shown and described, but is to beaccorded the widest scope consistent with the principles and novelfeatures herein disclosed. In other instances, well-known methods,procedures, and components have not been described in detail so as notto obscure the present invention. It is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

The invention relates to additive manufacturing (AM) in general, and inparticular to degradable materials for use in AM, for example, forproviding a temporary support structure for supporting 3D objects duringthe 3D building process, or otherwise as a building material inapplications that require temporary structures, such as investmentcasting or biomedical applications, such as, temporary implants and drugdelivery devices.

Additive manufacturing systems (AMS) and processes thereof generallyfabricate 3D objects in a layer-wise manner by forming a plurality oflayers in a configured pattern corresponding to the shape of theobjects.

Each layer is formed by an AMS such as a 3D printing apparatus, whichscans a two-dimensional surface and patterns it. While scanning, theapparatus visits a plurality of target locations on the two-dimensionallayer or surface, and decides, for each target location or a group oftarget locations, whether or not the target location or group of targetlocations is to be occupied by building material, and which type ofbuilding material is to be delivered thereto, e.g. modeling material orsupport material. The decision is made according to a computer image ofthe surface.

The apparatus deposits, e.g. jets via inkjet printing head, buildingmaterials in target locations which are to be occupied and leaves othertarget locations void. The apparatus typically includes a plurality ofdispensing heads, each of which can be configured to dispense adifferent building material. Thus, different target locations can beoccupied by different building materials.

The types of building materials can be categorized into two majorcategories: modeling material and support material. The modelingmaterial is generally a composition which is formulated for use in AM toform a 3D object. The support material serves to provide a supportstructure for supporting the object e.g. overhanging object parts duringthe fabricating process and/or other purposes, e.g., filling voids, toprovide hollow or porous objects.

Generation of the 3D support structure is performed according to thegeometry of the object in question, using designated software algorithmswell known in the art.

While a soluble material is physically dissolved in a dissolving mediumwithout any chemical reaction taking place, the degradable materialdescribed in this invention, undergoes a chemical reaction, which allowsa dissolving process to take place. Furthermore, the degradable materialof this invention undergoes degradation by means of reaction betweencomponents in the degradable material, which change the chemical natureof the material by means of chemical bond cleavage. The term “chemicalbond” as used herein relates to covalent bonds, ionic bonds, hydrogenbonds and Van der Waals bonds.

The terms “degradable material solution” or “material solution” as usedherein relate to a solution for use in AM process that comprises atleast one degradable component, which may be degraded by the meansdetailed herein. Further, the solution may include additionalcomponents, as detailed herein below. The material solution, in someembodiments of the invention, detailed below, may comprise adisintegrating agent.

The term “disintegration agent solution” used herein relates to asolution comprising a disintegrating agent, such as, without limitation,an enzyme, an acid, a base or a catalyst responsible for the selfdegradation of the self degradable material, which is also termed heredegradable material, of this invention. Further, the disintegratingagent solution may include additional components, as detailed hereinbelow.

The terms “degradable support material” or “support material” usedherein relate to any self degradable material produced via AM processand used as a support material.

An embodiment of the present invention is directed to a self degradablematerial produced by 3D printing by combining a degradable materialsolution and a disintegration agent solution before, during or afterdeposition of the solutions containing them. The degradable materialcombination thus produced comprises a degradable component and adisintegrating agent. The degradable component is a molecular structuralelement, which is chemically disassembled by the disintegrating agent,as or after they come into contact in the degradable material.

In an embodiment of the invention, the invention provides a materialsolution, comprising a degradable component for producing a supportmaterial during a layer-by-layer AM process or for making a mold for usee.g. in investment casting. In an embodiment of the invention, thematerial solution is deposited in liquid form, layer by layer, to form adesired geometry of a support construction or mold. Following thedeposition of each layer, the material solution is hardened, cured orsolidified, and the deposition-hardening sequence is repeated as neededuntil the target structure is completed.

The degradable material may comprise any type of degradable componentand may easily be removed from an object, for example by mechanical,chemical, thermal or a combination of such means. The material providingthe structure, e.g. a support structure, must be capable of providingthe required steadiness and firmness to hold layers or parts of layersof an object being prepared using the modeling material.

In an embodiment of the invention, the materials forming the degradablematerial or support are in a liquid form before deposition, both at roomtemperature and at jetting temperature, which is a higher temperaturethan room temperature and is, in an embodiment of the invention, in therange of 40° C.-75° C. and in another embodiment, is about 40° C. Thedegradable material or support material is hardened or solidifies tobecomes solid, semi-solid or a form of gel after deposition, for exampleby UV irradiation.

In an embodiment of the invention, the degradable component is acopolymer, which is disintegrated in a predictable timely manner, bycontacting the copolymer with a disintegrating agent.

In an embodiment of the invention, the disintegrating agent or thedisintegrating agent solution gradually degrades the degradablecomponent, so that the structure of the self degradable material turnsinto a liquid, a weak gel or small solid or gel particles, which arethen easily separable from the fabricated object, once thedisintegrating process comes into effect.

In an embodiment of the invention, the degradable component is acopolymer, which has at least one hydrophilic domain and at least onehydrophobic domain (amphiphilic copolymer) containing at least one typeof target region that can be cleaved in the presence of any appropriateactive substance such as a disintegrating agent. Using amphiphiliccopolymers may be desirable, because enzymes require a hydrophilicaqueous environment to maintain their activity, while usually degradinghydrophobic molecular sequences. The amphiphilic copolymers allowsolubilizing hydrophobic molecular regions in aqueous systems and createan environment that permits the processes of enzymatic cleavage anddegradation.

According to one embodiment of the invention, the copolymer is a blockcopolymer. Non limiting examples for copolymer components arepoly(ethyleneglycol) (PEG), poly(acrylic acid), poly(hyaluronic acid),poly(caprolactone) or poly(vinyl alcohol), dextran, cellulose, starch oralginate.

The disintegrating agent may be an enzyme that is able to cleave certainbonds in the degradable component, thereby causing it to turn to liquid,gel or small solid or gel particles that are easily removed from theprinted object material. Non-limiting examples of disintegrating agentsinclude enzymes such as esterase, which may cleave ester bonds in thecopolymer, cellulase, for cleaving cellulose bonds or dextranase forcleaving dextran bonds. In some embodiments, the esterase may be alipase. In an embodiment of the invention, the disintegrating agent isan acid, such as chloric acid, perchloric acid, citric acid, formicacid, nitric acid, phosphoric acid or sulfuric acid. In an embodiment ofthe invention, the disintegrating agent is a base, such as sodiumhydroxide, potassium hydroxide, barium hydroxide or magnesium hydroxide.

In an alternative embodiment of the invention, the disintegrating agentmay be combined within the modeling material forming the object. Thematerial comprising a degradable component forms a support construction,optionally with a modeling material grid within said supportconstruction adjacent to the object. When printing is complete, thedisintegrating agent is released into the adjacent support material anddegrades the degradable component, but not the modeling material,thereby weakening the support construction, at the interface between themodel material and support material enabling easy removal of the supportconstruction.

The disintegrating agent solution may be contacted with the degradablecomponent, according to some embodiments of the invention, at differentstages of the process, i.e. before the jetting (i.e. deposition), duringthe jetting or after the jetting.

Reference is now made to FIG. 1, according to which in one embodiment,the disintegrating agent solution (4) may be contacted with thedegradable material (3) during the fabrication or printing process,wherein each material enters and is deposited by a different printinghead (1 and 2) and come into contact, e.g. are combined within a layer,on the printing tray (10) or printing surface upon which the patternedlayers are being printed, e.g. the uppermost layer or surface of theobject being printed (printed object (9)).

Reference is now made to FIG. 2, according to which in anotherembodiment of the invention, the disintegrating agent solution (4) maybe contacted with the degradable material (3) a number of minutes orseconds before entering the printing head (1).

Reference is further made to FIG. 3, according to which in anotherembodiment, the disintegrating agent (4) may be included in thecartridge (7) together with the degradable material (3) in an isolatedstate such as for example, encapsulated or in an inactive form, and thecombined material deposited together via printing head (1) onto printingtray (10) or uppermost surface of printed object (9). The disintegratingagent (4) may be activated or released during the printing process orafter printing is complete by an external trigger, such as, for example,without limitation, heat, microwave radiation or ultrasound.

If necessary, the degradable component may be dissolved in appropriatesolvents in order to prepare a jetting-compatible formulation. In someembodiments, non reactive solvents such as, for example, withoutlimitation, water or alcohol, polyols or PEG, may be used. When suchnon-reactive solvents are used the concentration and the properties ofthe degradable component should be such to produce a material having therequired stiffness for acting for fulfilling the desirable application,i.e., sufficient stiffness for building a support material according tothis invention. If reactive solvents, such as acryloyl morpholine (ACMO)are included in the degradable material, the degradable componentconcentration used can be lower. However, the addition of reactiveingredients, such as reactive diluents, that are not sensitive to thedisintegrating agent can delay or even prevent the desirabledecomposition of the self degradable material. Therefore reactiveingredients, such as reactive diluents, should be added in appropriateconcentrations.

In an exemplary embodiment of the invention, there is provided adegradable component such as a block co-polymer composed ofPoly(ethylene glycol) (PEG) and poly(caprolactone) (PCL) domains, whichcontains photo-polymerizable functional groups (difunctional), such asacrylates or methacrylates. The use of monofunctional polymers ispossible but considered less effective, because they will not contributeto the network cross link density. The backbone of the polymer created,for example, by the reaction of acrylic functional groups will usuallynot be cleaved by the disintegrating agent. In an embodiment of theinvention, these molecules may be dissolved in organic (non-polar)and/or in aqueous (polar) solvents, depending on the specific PEG/PCLratio, and then photopolymerized to form a solid or a gel. The PCLdomain contains ester bonds that can be cleaved by hydrolysis in a basicenvironment or by an appropriate enzyme, usually esterase, even in aneutral pH, wherein the base or the enzyme act as the disintegratingagent according to this invention. Cleaving the ester bonds inside thecross-linked hydrogel results in decreasing the stiffness of the solidor gel material and/or its conversion into liquid, so that the materialis easily removed. According to some embodiments, the disintegratingagent is added to the copolymer shortly before the polymerization andinitiates gradual degradation of the formed degradable material.

Specifically, in an embodiment of the invention, a PCL750-PEG1500-PCL750 tri-block copolymer is synthesized from PEG 1500 gr/mol ofvarious lengths and c-Caprolactone as described in FIG. 6, in thepresence of Stannous 2-Ethyl-Hexanoate, using any appropriate procedureknown in the art. The tri-block copolymer is functionalized withacrylates to result in tri-block di-acrylate molecules. These moleculesare then dissolved in a mixture of water and benzyl alcohol to receive a25% (w/v) tri-block copolymer solution, acting as the degradablematerial solution according to this invention.

The viscosities of the degradable material solution should be in therange that is suitable for ink-jetting, namely, under 30 cP, or undercertain embodiments, between 10 cP and 20 cP at jetting temperaturesbetween about 25° C. to 80° C. A 0.1% to 0.3% of a surfactant, forexample BYK 345, may be added to the degradable material solution toadjust the surface tension of the formulation to 25 mN/m-35 mN/m inorder to allow its implementation in ink-jet systems. Between 0.5% to 3%of photoinitiator, for example, Irgacure 2959 (Ciba), may be added tothe degradable material solution to allow the photopolymerization of thetriblock copolymers. Polymerized hydrogel having compressive modulusbetween 100 KPa and 1000 KPa may be produced, appropriate for use as forexample support material or degradable material. Generally, theviscosity of the solutions may be measured by any means known in theart, including shear rheometry or viscometry. In some embodiments asupport material or degradable material were produced. Such supportmaterial or degradable material having overall, physical properties,jetting behavior, polymerization kinetics and gel properties comparableto those of a conventional support material that is currently used inObjet printers, e.g. FullCure® 705.

According to one embodiment, and as exemplified in example 4, thepolymerized hydrogel, which is the degradable material according to thisinvention, is converted into liquid when exposed to a solution ofPseudomonas lipase having a concentration of at least 1 mg/ml.

In an embodiment of the invention, a disintegrating agent solutioncontaining 1-5 mg/ml of Pseudomonas lipase in a solvent containing30%-70% water, 10-30% Glycerol, 0-40% PEG400 and 0.05-0.3% BYK 345, isprepared. This solution may be deposited together (in parallel) with thedegradable material solution as a designated ‘combined material’ or“Digital Material” (DM) using for example a multi-material 3D printersuch as Connex™ 500 system (Objet Geometries Ltd.). 3D printing ofmultiple materials, using for example Connex™ 500 system, allows thedesign of materials at the voxel level, where for example a degradablematerial solution and a disintegrating solution may be digitallycombined, meaning that a software file will describe the materialstructure at the voxel level. For example, according to this embodiment,a degradable material containing small regions for example, ofinclusions of disintegrating agent may be designed. Such combinedmaterial comprises a continuous phase of degradable material made, e.g.of a support material with, for example, small regions of between0.03×0.03×0.03 mm and 0.5×0.5×0.5 mm of disintegrating agent,disseminated into the degradable material at a level of for examplebetween 0.01% disintegrating agent or 0.1% or 1% or 10% or anyconcentration of the disintegrating agent solution according to theintended use and required properties of the resulting degradablematerial, e.g. rate of degradation. In an exemplary embodiment, phases,e.g. regions made of the disintegrating agent solution, may be distancedfrom one another within the continuous degradable material phase, suchthat the distance between the phases is kept, for example, below one cmin each direction and the overall volumetric ratio of the disintegratingagent solution is between 0.01% and 10%. The printing of such DM usingthe standard Connex process may result in hydrogel layers that areconverted into liquid after between 1 hour and 72 hours following thedeposition. A dedicated software is used to calculate the volume ratioof the disintegrating agent solution in order to provide the desirabledecomposition kinetics.

In another embodiment, the disintegrating agent solution is delivered tothe printing apparatus from a cartridge and mixed or combined with thedegradable material solution before jetting, just before entering theinkjet printing heads of the apparatus. Dedicated software together witha dedicated automated pump system and an appropriate mixing chamber,e.g. in proximity of the printing heads, are used to dynamically producea homogeneous mixture of the degradable material solution with between0.01% (v/v) and 10% (v/v) of the disintegrating agent solution, which isthen delivered to the printing heads. The printing of such mixturesresults in hydrogel layers that are gradually converted into soft gel orliquid after between 1 hour and 72 hours following the deposition.

In another embodiment of the invention, in cases that the degradablematerial solution includes degradable polysaccharides (for example, oneshaving acrylate functional groups) that can be degraded by appropriateenzymes, functioning as the disintegrating agent. Examples for suchmaterials may include acrylated and/or modified polysaccharides, such asstarch, cellulose, dextran, chitosan or alginate.

In another embodiment, the degradable material includes reactivepolymer-protein hybrid molecules (for example, having acrylatefunctional groups) that can be degraded by appropriate enzymes, such astrypsin, collagenase or plasmin.

In another embodiment, biosynthetic hydrogel materials can be used forpreparing the degradable material solution. Biosynthetic hydrogelmaterials consist of a protein or a peptide that is conjugated withpolymer chains terminated by acrylate end groups. An example of such amaterial is bovine albumin protein that is modified with PEG-acrylatepolymer chains using a widely implemented method called PEGylation. Themolecular weight of the PEG-acrylate polymer chains may be between10,000 and 20,000 gr/mol. Each protein molecule should be modified withbetween 50 to 100 PEG-acrylate chains. The resulting material, namelyPEGylated Albumin Acrylate (PAA), may be used according to thisinvention for preparation of enzymatically degradable material.According to certain embodiments, the degradable material solutioncomprises 15-30% of PAA, 65-80% water, 1-4% photoinitiator (for example,without limitation, Irgacure 2959, Ciba) and 1-6% of additives,including viscosity modifiers, rheology modifiers and surfactants,ensuring that the degradable material solution will be compatible withexisting deposition systems, such as three dimensional ink jet printing.According to the present invention, the liquid degradable materialsolution described above is mixed with a concentrated (0.01-10 mg/ml)solution of protease enzyme, such as trypsin or pepsin in water, whichacts as the disintegrating agent solution. These enzymes cleave thealbumin protein and disintegrate the hydrogel network structure. Themixing ratio (degradable material solution: disintegrating agentsolution) is between 10000:1 and 100:1. The optimal ratio depends on thedesired degradation rate, as described hereinafter according to therequired time or rate of degradation (depending on specificobject/printing tray print time, the nature of the degradable materialsolution, the nature of the disintegrating agent solution, the pH of thedisintegrating agent solution, the type of enzyme and its activity, andthe like). The mixing ratio may be sampled and determined according tothe judgment of one skilled in the art. Generally, the degradation ofthe material may be measured by pH changes, viscosity changes, massloss, etc.

In another embodiment, the degradable material contains linear orbranched poly(ethylene glycol) (PEG) that is modified with at least twoacrylate/methacrylate functional groups and having molecular weightbetween 1000 to 20000 gr/mol. It is dissolved, for example, in a mixtureof water, PEG400 and/or PE600 and/or Glycerol and BYK345 to obtain aformulation that is suitable for ink-jetting. This material is used witha disintegrating agent that is composed of an ink-jet formulation thatcontains a weak base or a strong base in such concentration that the pHof the degraded media (degradable material or the support materialtogether with disintegrating agent) will be between 13 and 14. At basicpH, the ester bonds of the PEG-acrylate undergo degradation byhydrolysis and the hydrogel stiffness is reduced.

In other embodiments, the degradable material solution is hardened byphase change from liquid to solid or gel or a semisolid form withoutphotopolymerization, i.e., the degradable material solution may comprisea wax. It may further be combined with additional components thatundergo photopolymerization to improve the performance of the degradablecomponent and the disintegration thereof.

As mentioned above, the hardening of the degradable material solutioninto a solid, gel or into a semi solid state and of the object materialmay be performed by a variety of methods, including UV curing, phasechange, drying and crystallization. Any of these methods may cause theinactivation of the disintegrating agent, which, according to thisinvention, must be overcome. In an embodiment of the invention, when thedisintegrating agent is inactivated, for example, by exposure to UV,and/or exposure to the ingredients of the degradable material, such asthe photoinitiator, the disintegrating agent solution may furthercomprise porous nanoparticles for preventing fast mixing of thedisintegrating agent with the degradable material solution. In such anembodiment, the disintegrating agent solution comprises a soluble phaseand solid or gel porous nanoparticle phase. The concentration of thedisintegrating agent in the porous nanoparticles and in the solublephase may be identical, but only the fraction found in the porousnanoparticles will survive the printing process. Therefore theconcentration of the disintegrating agent solution should be calculatedaccordingly.

In an alternative embodiment, in order to prevent the above describedinactivation, the disintegrating agent solution may contain adisintegrating agent that is dispersed in a solvent that is immisciblewith the solvent of the degradable material solution.

In an alternative embodiment, in order to prevent the above describedinactivation, the disintegrating agent solution may contain reactivecomponents that may cause polymerization or hardening of thedisintegrating agent solution. The disintegrating agent solution is thendeposited and polymerized at each layer separately from the degradablematerial solution. In such a way, the disintegrating agent solution canform hydrogel particles that do not mix completely with the degradablematerial solution and that may release the disintegrating agentgradually by diffusion.

In an alternative embodiment, the disintegrating agent solution containsa disintegrating agent that is encapsulated in smart carriernanoparticles that are dispersed throughout the degradable materialsolution prior to the printing process. The disintegrating agent isisolated and does not affect the properties of the material solution.According to certain embodiments, the disintegrating agent is releasedduring the printing process, or after the printing process using aspecific trigger, such as heating, microwave irradiation, lightirradiation, ultrasound or sonication.

Other proteins and polymers can also be used for preparation of thedegradable materials. The selection of the protein and polymer should bebased on empirical observations in which the prepared biosyntheticdegradable material is cross-linked to form a hydrogel and then immersedin an enzyme solution (with a concentration of about 0.1 mg/ml), i.e., adisintegrating agent solution. The enzyme should be known to be able tocleave each protein in at least one site. If after one week at 37° C.the hydrogel stiffness (i.e. compressive modulus) is reduced at least100 times, then the protein-polymer combination can be used forsynthesis of the degradable material. The appropriate hydrogelcomposition and enzyme concentration can be determined empirically bymixing the hydrogel precursor solutions with enzyme solutions atdifferent ratios and measuring time required for the hydrogeldisintegration.

Reference is now made to FIG. 4, relating to the automateddisintegration of the degradable component. For optimal performance,according to certain embodiments, an automatic system can be used tocontrol actual disintegrating agent concentration in each depositedlayer (slice). This allows synchronizing the stiffness reduction ofdifferent layers and combining acceptable performance during printingwith desirable rate of degradation after the printing ends. Suchautomatic synchronization system includes the following components (asdepicted in FIG. 2, relating to a system wherein the disintegratingagent solution and the degradable material solution are mixed beforeentering the printing head): 1. a cartridge which include a concentrateddisintegrating agent solution; 2. a cartridge with the degradablematerial solution; 3. two computer-controlled liquid pumps that transferthe degradable material solution and the disintegrating agent solutioninto a dual component mixing chamber; 4. a mixing chamber that receivesand homogenizes the degradable material and disintegrating agentsolutions and then transfers the mixture into the printing block; 5. acomputer program that uses the specific print job data, including traysize, object size and print speed, as well as degradation kinetics data,namely a calibration curve that correlates between disintegrating agentsolution concentration and the time that takes for the material to reachits performance limit, to calculate the required disintegrating agentsolution concentration. In some embodiments, where the degradablematerials is intended to perform as support material, the performancelimit is based on minimal stiffness requirements for adequateperformance, e.g. support performance, which are determined according tospecific depositing technology, but usually require compressive modulusof about 0.3-1.0 MPa. The appropriate disintegrating agent solutionconcentration should form a material layer with a compression Youngmodulus at the end of the print job that is about 10% higher than theperformance limit value.

The system operation is described in FIG. 4, relating to automatedscheduling of degradation. This figure presents an example of printingof tray consisting of 100 slices and containing degradable supportstructure. The stiffness of the first slice (Slice 1) should remainabove the performance limit for the whole print duration, therefore itshould contain low enzyme concentration that will reduce its stiffnessslowly (moderate slop at the figure). The last slice (Slice 100), on theother hand, does not require a prolonged performance period, andtherefore it should contain the highest possible enzyme concentrationthat will cause a steep reduction of its stiffness over time. Thescheduling of degradation will reduce the time from the “print finish”step to “part clean” step, when compared to a constant (consistent)enzyme concentration approach. Moreover, increasing the gap between thesupport stiffness to the performance limit stiffness will also reducethe support removal time, when using the scheduled degradation approach.

The dynamic modulation of the disintegration agent'concentration, e.g,enzyme concentration in different slices can be achieved also using theDigital Materials concept. The printed pattern that includes areas orphases made of the degradable material and areas or phases made of thedisintegrating agent can be modified by automatic software to receivedifferent mixing ratios and result in more convenient degradationkinetics.

According to one embodiment, the degradable material or the supportmaterial mechanical properties, including compressive modulus,compressive strength and strain to break can be increased by addingrigid reinforcement. Such reinforcement includes the use of a materialthat is used for an object formation and usually consists of UV curablematerial with compressive modulus above 1 GPa. This material can bedeposited in such a way that the resulting degradable material or thesupport material will generally include about 10-30% w/w of rigidregions having side length between 0.2 to 1.0 mm. Differentreinforcement geometries can be used for optimal support performance.

According to one embodiment, the above described degradable material canbe used not only as a support material, but also as an object material,for example for replacing wax in investment casting, acting as atemporary implant or a drug delivery device.

EXAMPLES Example 1 Lipase Activity on PCL

Electrospun PCL was added to solutions of three lipases derived fromPseudomonas, Candida and Porcine pancreas lipases. Each solutioncomprised 1, 2, or 4 mg/ml of one of the lipases. As shown in FIG. 5,PCL specimens added to Pseudomonas lipase solutions were degraded aftertwo hours of incubation, while the two other lipases did not degrade thePCL.

Example 2 Triblock Polymer Solution Viscosities

As demonstrated in FIG. 6, triblock polymers PCL-PEG-PCL weresynthesized from PEGs of various lengths and c-Caprolactone, in thepresence of Stannous 2-Ethyl-Hexanoate. After synthesis, samplemolecular structures were analyzed by NMR.

Three triblock polymer species were synthesized:

-   -   1. PEG 4000Da: PCL_(1000Da)PEG_(4000Da)PCL_(1000Da)    -   2. PEG 6000Da: PCL_(1000Da)PEG_(6000Da)PCL_(1000Da)    -   3. PEG10000Da: PCL_(1000Da)PEG_(10000Da)PCL_(1000Da)

Viscosities were measured in 20% polymer solutions in water, eachcomprising one of the above three polymers, as a function of shear rateat 25° C. The results are shown in FIG. 7.

The results shown in FIG. 7 teach that a triblock solution is a shearthinning non-newtonian fluid. Further, the solution viscosity is highlydependent on polymer length, where longer polymer chains cause anincrease in viscosity.

Time sweep tests were performed at 25° C. at shear rates of 10sec-1 and50sec-1 and at 40° C., 10sec-1. These time sweeps are shown in FIGS. 8a, 8 b and 8 c, respectively.

The initial viscosity values of the three 20% solutions are given inTable I below:

TABLE I Triblock with Tri-block with Tri-block with PEG 10000Da PEG6000Da PEG 4000Da {dot over (γ)} = 10 sec⁻¹, 6.9 [Pa · sec] 1.9 [Pa ·sec] 0.19 [Pa · sec] v_(max) = 5 mm/sec. T = 25° C. {dot over (γ)} = 50sec⁻¹, 5.1 [Pa · sec] 1.5 [Pa · sec] 0.19 [Pa · sec] v_(max) = 25 mm/secT = 25° C. {dot over (γ)} = 10 sec⁻¹, 2.2 [Pa · sec] 0.7 [Pa · sec] 0.17[Pa · sec] v_(max) = 5 mm/sec T = 40° C.

The viscosity measurements detailed above and presented in FIGS. 7, 8 a,8 b and 8 c and Table I, teach that the triblock solution isnon-newtonian, changing its internal organization under shear stress,which results in an increase in the viscosity with time. Higher shearrate results in lower viscosity due to the shear thinning nature of thesolution. Further, as shown in Table I, the initial viscosity values aretemperature dependent, decreasing with temperature.

Acrylated Triblock Polymer Solution Viscosities

The viscosity of acrylated triblock polymers was compared to that of thesame triblock polymers prior to acrylation.

Three block copolymers where used:

-   -   1. acrylated PCL_(1000Da)PEG_(4000Da)PCL_(1000Da)    -   2. acrylated PCL_(500Da)PEG_(4000Da)PCL_(500Da)    -   3. acrylated PCL_(750Da)PEG_(1500Da)PCL_(750Da)

It was found that a solution of acrylatedPCL_(1000Da)PEG_(4000Da)PCL_(1000Da) was significantly more viscous thanthe triblock polymer prior to acrylation. This may be due to loss ofhydroxide groups at the edges of the molecule and resulting increase inhydrophobic interactions. The viscosities ofPCL_(1000Da)PEG_(4000Da)PCL_(1000Da) after and before acrylation(compared to support material), are shown in FIGS. 11 a and 11 brespectively.

As seen in FIG. 11 a, the viscosity of acrylated

PCL_(1000Da)PEG_(4000Da)PCL^(1000Da) was too high for use as maindegradable copolymer according to this invention.

The viscosity of PCL_(500Da)PEG_(4000Da)PCL_(500Da) which has shorterPCL fragments, and as a result is less hydrophobic.

PCL_(750Da)PEG_(1500Da)PCL_(750Da)—this triblock has shorter PEGfragments, to reduce entanglement. The PCL fragments were also shortenedin order to allow dissolution in water.

The viscosities of 20% solutions of the above last two polymers weremeasured as a function of shear rate, before and after acrylation. Theresults of these measurements are shown in FIGS. 12 a and 12 b. Further,the time sweep tests of the same solutions were compared to those of thesupport at 25° C. (before and after acrylation) and at 40° C. (afteracrylation) at a shear rate of 50sec-1. The results of the time sweepsare shown in FIGS. 13 a, 13 b and 13 c.

As shown in the above figures, both of these triblocks are less viscousthan the support material at room temperature. The acrylation effect onviscosity is less significant than inPCL_(1000Da)PEG_(4000Da)PCL_(1000Da), andPCL_(750Da)PEG_(1500Da)PCL_(750Da) is less viscous thanPCL_(500Da)PEG_(4000Da)PCL_(500Da), however, it is not Newtonian.

The initial viscosity values of the support of several solutions aregiven in Table II below:

TABLE II 25° C. 40° C. Support 95 49 PEG-DA 10000Da 20% 16 11PCL_(1000Da)PEG_(4000Da)PCL_(1000Da) 10% 78 112PCL_(1000Da)PEG_(4000Da)PCL_(1000Da) 20% 21800PCL_(500Da)PEG_(4000Da)PCL_(500Da) 30% 127 65PCL_(500Da)PEG_(4000Da)PCL_(500Da) 20% 32 18PCL_(500Da)PEG_(4000Da)PCL_(500Da) 15% 10 6PCL_(750Da)PEG_(1500Da)PCL_(750Da) 30% 672 1800PCL_(750Da)PEG_(1500Da)PCL_(750Da) 20% 16 Value not stable near t = 0,reaches 14

As seen in Table II, both of the new acrylated triblocks have low enoughinitial viscosity values at 20% solutions, wherein the upper viscositylimit was defined as 18 cP.

Example 3 Triblock Degradation by Lipase

The degradation of the triblocks, prepared according to Example 2 (PCLadded to PEG4000Da, PEG6000Da and PEG10000Da), was monitored in twoways: 1) by measuring pH change with time after lipase addition; and 2)by measuring the change in viscosity with time.

PCL monomers are acids, and therefore, as the PCL polymers degrade, thepH of the solution is expected to drop. Additionally, the solutionviscosity is expected to decrease with degradation, since the length ofthe polymers becomes shorter.

The following experiments were conducted with the lipase enzymeextracted from Pseudomonas cepacia (Sigma 62309, BioChemika, powder,light beige, ˜50 units/mg).

Change in pH During Degradation

10% solutions of the three triblock polymers in water were degraded bythe addition of 0.5 mg/ml of the lipase. The pH change of the solutionswas monitored both by addition of phenol red (red in neutral solutionsand yellow in acidic solutions) and by using a pH-meter.

The measurements showed that there is a significant pH decreaseimmediately after lipase addition, which continues with time. This isevidence of triblock degradation by the enzyme. Further, differences inthe degradation kinetics of the three polymer types were not evident inthe pH tests.

Change in Viscosity During Degradation

A change in the triblock solution viscosity with time was measured atshear rate of 10 sec-1, after addition of 0.1 mg/ml lipase. The resultsare shown in FIG. 9. As evident in FIG. 9, there is a time delay, whichresults from mixing and experiment preparation. Further, the initialpoint was measured by testing the solutions at the same temperature andshear rate, though with no lipase addition.

FIG. 10 shows the viscosity variation of PEG 6000Da triblock after theaddition of various lipase doses, specifically, no lipase, 0.1 mg/mllipase and 1.0 mg/ml lipase.

As evident from FIG. 9, there is a difference between the threetriblocks in degradation kinetics. The triblock with the shortest PEG isthe one with the fastest degradation due to higher PCL percentage.Further, as evident from FIG. 10, the degradation kinetics is dosedependant, allowing controlling of degradation time by lipaseconcentration variation.

Example 4 Hydrogels

Mechanical Properties

Hydrogels were prepared from the acrylated tri-block solutions detailedin Example 2 by exposure of the solutions to UV radiation. Thecompression moduli of the hydrogels, obtained from Instron® measurementsand G′ values obtained from rheology are provided in Table III below.

TABLE III Compression modulus [KPa] G′ [KPa] FullCure ® 705 328 ± 41  107 PEG 20000Da 30% 188 ± 19 KPa PEG 10000Da 30% 295 ± 27 KPa PEG10000Da 20% 154 ± 10 KPa 54 PCL_(1000Da)PEG_(4000Da)PCL_(1000Da) 10% 20± 2 KPa 5.8 PCL_(500Da)PEG_(4000Da)PCL_(500Da) 30% Was not Was notmeasured, measured, since the since the modulus modulus was above thewas above the instrument instrument limit, i.e., limit, i.e., higherthan higher than 328KPa. 328KPa. PCL_(500Da)PEG_(4000Da)PCL_(500Da) 20%294 ± 11 KPa 112 PCL_(500Da)PEG_(4000Da)PCL_(500Da) 15% 48PCL_(750Da)PEG_(1500Da)PCL_(750Da) 30% 234 ± 20 KPa 105PCL_(750Da)PEG_(1500Da)PCL_(750Da) 20% 76 ± 3 KPa 26

As shown in Table III, gels formed after crosslinking ofPCL_(500Da)PEG_(4000Da)PCL_(500Da) 20% andPCL_(750Da)PEG_(1500Da)PCL_(750Da) 30% have stiffness comparable toFullCure® 705 support material. However, as can be seen in Table II, theviscosity of PCL_(750Da)PEG_(1500Da)PCL_(750Da) 30% is too high, i.e.,above 18 cP, set in this example as the upper viscosity limit.

Curing Kinetics at 5 mW/cm

Curing times for various hydrogels that may be used for printing incomparison to FullCure® 705, and related to herein as the “support” areprovided in Table IV below. Curing time was taken as the time needed toreach 90% of maximum G′ value.

TABLE IV Curing time [sec] Support 44 PEG 20000Da 20% 191 PEG 10000Da20% 197 PCL_(1000Da)PEG_(4000Da)PCL_(1000Da) 10% 121PCL_(500Da)PEG_(4000Da)PCL_(500Da) 20% 158PCL_(500Da)PEG_(4000Da)PCL_(500Da) 15% 170PCL_(750Da)PEG_(1500Da)PCL_(750Da) 30% 164PCL_(750Da)PEG_(1500Da)PCL_(750Da) 20% 136

Curing times for the hydrogels are long, compared to the support;however they may be shortened by increasing their photo-initiatorconcentration or UV intensity.

Hydrogel Degradation by Lipase

The hydrogels listed in Table V, were degraded in solutions containinglipase. Degradation took about 12 hours. It was found that onlyPCL_(750Da)PEG_(1500Da)PCL_(750Da) andPCL_(1000Da)PEG_(4000Da)PCL^(1000Da) were degraded by the lipase.

Mass Loss During Curing

Mass loss, which is defined as the difference between the solutionweight before the polymerization and the hydrogel weight afterpolymerization, after the excess of liquids was removed, used to measurethe gel contraction during the polymerization, is shown in Table V. Noconnection between hydrophobicity and mass loss is evident, teachingthat mass loss is mostly dependent on curing conditions.

Table V Mass loss during curing % PCL_(1000Da)PEG_(4000Da)PCL_(1000Da)10% 16 PCL_(500Da)PEG_(4000Da)PCL_(500Da) 15% 18PCL_(750Da)PEG_(1500Da)PCL_(750Da) 20% 12 PEG 10000Da 20% 20

What is claimed is:
 1. A three dimensional printing method for producinga self-destructible temporary structure, comprising: depositing adegradable material solution comprising a degradable component;depositing a disintegrating agent solution comprising a disintegratingagent capable of disintegrating the degradable component; solidifying acombined disintegrating agent and degradable material solution to form asolid, semi solid or gel layer; and repeating said steps of depositingand solidifying layers until the self-destructible temporary structureis formed, wherein after solidification, the disintegrating agentgradually degrades the degradable component to disintegrate theself-destructible temporary structure.
 2. The method of claim 1 whereindepositing the degradable material solution and the disintegrating agentsolution is done by one or more inkjet printing heads.
 3. The method ofclaim 1, wherein the disintegrating agent solution and the degradablematerial solution are combined immediately before deposition.
 4. Themethod of claim 1, wherein a combination of the disintegrating agentsolution and the degradable material solution occurs after deposition,within a deposited layer.
 5. The method of claim 1, wherein thedisintegrating agent is an enzyme, catalyst, acid or a base.
 6. Themethod of claim 5, wherein the enzyme is an esterase, a trypsin, acollagenase, a cellulase or a dextranase.
 7. The method of claim 1,wherein the disintegrating agent is in an isolated state and wherein thedisintegrating agent is released and activated during or afterdeposition of a three-dimensional printing process by an externaltrigger.
 8. The method of claim 1, wherein the degradable component is aphotopolymer, a wax or a combination thereof.
 9. The method of claim 1,wherein the degradable component is a polymer.
 10. The method of claim9, wherein said polymer is a copolymer, a block-copolymer, aphotopolymer, a polysaccharide, reactive polymer-protein hybridmolecules, a biosynthetic hydrogel material or a wax.
 11. The method ofclaim 10, wherein said copolymer comprises polyethyleneglycol (PEG) orpoly(acrylic acid) or poly(hyaluronic acid) or polycaprolactone orpoly(vinyl alcohol).
 12. The method of claim 1, wherein the degradablematerial solution further comprises any one of a reactive solvent, anon-reactive solvent, a surfactant, a photoinitiator, a viscositymodifier, a rheology modifier or any combination thereof.
 13. The methodof claim 1, wherein the disintegrating agent solution further comprisesany one of a reactive solvent, a non-reactive solvent, a surfactant, aphotoinitiator, porous nanoparticles, a viscosity modifier, a rheologymodifier or any combination thereof.
 14. The method of claim 1, whereinthe disintegrating agent decomposes at least one chemical bond or atleast one physical bond within the degradable component.
 15. The threedimensional printing method of claim 1, wherein combination of thedisintegrating agent solution and the degradable material solution iscontrolled by a dedicated software so that the volumetric ratio betweenthe degradable material solution and disintegrating agent solution canbe modulated during printing.
 16. The three dimensional printing methodof claim 1, wherein the disintegrating agent solution comprises a liquidphase that is insoluble in the degradable material solution.
 17. Thethree dimensional printing method of claim 1, wherein the disintegratingagent solution comprises a solid or gel phase that is insoluble in thedegradable material solution.
 18. The three dimensional printing methodof claim 1, wherein the disintegrating agent solution comprisesnanoparticles filled with the disintegrating agent and thedisintegrating agent is released by an external trigger.
 19. The methodof claim 1 comprising: controlling disintegrating agent concentration ofthe disintegrating agent in each deposited layer based on desirablerates of degradation for each of the deposited layers, wherein thedisintegrating agent concentration within a first deposited layer islower than the disintegrating agent concentration in an upper depositedlayer.
 20. The method of claim 1, wherein the self-destructibletemporary structure provides support for a three-dimensional objectduring building of the three-dimensional object by a three-dimensionalinkjet printing system.